1. Field of the Invention
The invention relates to a refining surface of a refining member for a refiner intended for defibrating lignocellulose-containing material, the refiner comprising at least two refining surfaces arranged coaxially relative to each other, at least one of which refining surfaces is arranged to rotate around a shaft, and between which refining surfaces the material to be defibrated is fed, and which refining surface comprises first bars extending from the inner circumference of the refining surface to the outer circumference of the refining surface and between them first grooves, and the upper surfaces of which first bars further comprise second grooves connecting said first grooves, and between which second grooves there are second bars.
The invention further relates to a blade segment of a refining member for a refiner intended for defibrating lignocellulose-containing material, the refiner comprising at least two refining surfaces arranged coaxially relative to each other, at least one of which refining surfaces is arranged to rotate around a shaft, and between which refining surfaces the material to be defibrated is fed, and which blade segment can be arranged to form at least a part of at least one refining surface, and which blade segment comprises first bars extending from the inner circumference of the refining surface to the outer circumference of the refining surface and between them first grooves, and the upper surfaces of which first bars further comprise second grooves connecting said first grooves, and between which second grooves there are second bars.
2. Description of Related Art
Disc and cone refiners used for treatment of fibrous material are typically formed of two or possibly more refiner discs or refining members opposite to each other which are arranged to turn relative to each other so that at least one of said refiner discs is arranged to rotate around a shaft. In disc refiners the refiner disc is disc-like and in cone refiners it is conical. In a refiner comprising two refiner discs, one of the refiner discs further comprises an opening through which the material to be refined is fed into the refiner. The part of the refiner disc where said feed opening is located can be called a feed end. The refiner discs are positioned in such a way that they form a refiner gap between them, where lignocellulose-containing material is defibrated. The distance between the refiner discs is largest on the feed side or at the feed point of the lignocellulose-containing material, i.e., in a disc refiner, in the middle of the discs, and in a cone refiner, at the cone end having a smaller diameter, said gap being reduced towards the discharge point or discharge side of the material to be refined in order to gradually grind the material to be refined.
The refining surfaces of refiner discs or refining members are typically formed of protrusions, i.e. blade bars, extending from the inner circumference or first radial edge of the refining surface to the outer circumference or second radial edge of the refining surface, and of grooves between the blade bars. Hereafter, blade bars are also called bars. The shape of these grooves and bars per se may vary in different ways. Thus, for example, in the radial direction of the refiner disc, the refining surface may be divided into two or more circular parts, each circular part having bars and grooves whose number and density as well as their shape and direction may deviate from each other. Thus, the bars may be either continuous over the whole length of the refining surface radius or there may be a plurality of separate, successive bars in the radial direction. At the refiner rotor, the bars and the direction thereof have a greater effect than at the stator because of the rotation of the rotor, whereby the fibrous material to be refined is subjected especially by the rotor bars to a refining force resultant which affects with a velocity determined on the basis of the radius and rotational speed of the refining surface. The bars of the stator form counter pairs or a counter surface for the rotor, required in refining, the blade bars crossing each other during refining like scissor blades. However, there is a small clearance between the rotor bars and stator bars of the refiner, and the fibrous material is mainly ground or refined between them.
Refining surfaces of refiner discs or refining members can be formed directly onto the surface of the refining discs for example by casting or by separate machining but usually a refining surface is formed of blade segments which are arranged next to each other on the refiner disc both in the radial and in the circular or angular direction of the refiner disc so that the refiner disc is provided with a uniform refining surface. Thus, each blade segment forms a part of the refining surface of the refiner disc.
In the case of a disc refiner, the inner circumference or first radial edge of the refining surface refers to the middle part of the refining surface and, in the case of a cone refiner, to the end of said cone with the smaller diameter. The outer circumference or second radial edge of the refining surface refers, in the case of a disc refiner, to the outer part of the refining surface, i.e. the part where the circumference of the refining surface is largest, and, in the case of a cone refiner, to the end of said cone with the larger end.
Attempts have been made earlier to improve the load capacity or refining capacity of refiners by increasing the combined length of the refining surface bars. As a result, such blade or refining surface solutions have been designed and used, where blade bars are located closer and closer to each other. In such “dense blades”, it is the volume or capacity of the grooves that determines the production capacity of the refiner blade. Due to the manufacture, blade bars typically have a clearance angle of 1 to 5°, which means that closer to the bottom of the groove the bar is thicker. This limits the groove volume even more. In addition, in cast blades the groove surfaces are rough, which causes flow resistance to the fibrous material to be refined. The narrower a groove is, the stronger becomes the flow resistance. A problem of these “dense blades” is, therefore, that they tend to be blocked. On the other hand, even the above mentioned blade solutions have not been successful in increasing the refiner capacity in a desired way.
U.S. Pat. No. 4,676,440 discloses a typical refiner blade for a high-consistency refiner. The blade formation of the publication consisting of blade segments is formed of three refining surface zones in the radial direction of the refiner disc, whereby in the outer zones of the refining surface the blade bars are positioned very close to each other in order to achieve a high refining capacity. Because of this, the volume of the grooves between the bars has become smaller. Therefore, on the refining surface of at least one of the refiner discs there is also one or more discharge channels having a substantially larger cross-section than said grooves in order to discharge steam generated during refining from between the refining surfaces. With these discharge channels, it has been possible to diminish the problems caused by steam generated during refining in the refining process, but the discharge channels may, however, make the refining more uneven and, in practice, the steam discharge channels described in the publication are arranged too sparsely with respect to each other.
U.S. Pat. No. 5,467,931 discloses a refining surface, wherein the efficiency of a refiner with densely arranged bars has increased due to a higher flow capacity of the refiner blades. Flow capacity has increased primarily because material has been chamfered away from the background edges of the blade bars. The publication also discloses a blade bar, the upper surface of which is provided with small grooves at sparse intervals, which can slightly increase the flow capacity of the grooves between the bars and facilitate the discharge of steam produced during refining from between the refining surfaces. Said grooves on the upper surface of the blade bar also add to the combined cutting length of the bars of the refining surface to some extent, but, in practice, the oblique structure of the upper surface of the blade bar hinders these small grooves from participating in the refining of the material before the blade bar has worn significantly, which means that one has not, nevertheless, succeeded in substantially increasing the refining capacity of the refiner.